JP 2001-152883A (Reference 1) discloses a technology in which a valve opening and closing timing control mechanism which sets respective opening and closing timings that correspond to intake valves and exhaust valves is provided, and in a case where a locked state cannot be released due to a failure or the like of the valve opening and closing timing control mechanism of the intake valve, the valve opening and closing timing control mechanism of the exhaust valve is controlled to the most advance angle phase.
In the technology described in Reference 1, in a case where a lock mechanism of the valve opening and closing timing control mechanism which controls the intake valve cannot be unlocked due to a failure or the like, and the opening and closing timing of the intake valve is fixed to an intermediate phase, a valve overlap is set to be small by controlling the valve opening and closing timing control mechanism of the exhaust valve to the most advance angle phase, and deterioration of a combustion state is suppressed by reducing an internal EGR.
In addition, JP 2016-70069A (Reference 2) discloses a technology in which an electric type valve opening and closing timing control mechanism for setting the respective opening and closing timings that correspond to the intake valve and the exhaust valve is provided, and in a case where the valve opening and closing timing control mechanism fails, control is performed such that an ignition timing is advanced or an overlap period is shortened.
In the technology described in Reference 2, startability of an internal combustion engine is improved by advancing the ignition timing, and a compression ratio is increased by shortening the overlap period.
In an internal combustion engine provided with a valve opening and closing timing control mechanism which operates hydraulically, there is also a case where the internal combustion engine is started in a situation where a hydraulic pump or a control valve fails and a hydraulic pressure of hydraulic oil becomes insufficient. In such a situation, not only the valve opening and closing timing control mechanism does not appropriately operate, but also the opening and closing timing (valve timing) set by the valve opening and closing timing control mechanism is displaced to the most delay angle by an action of a cam fluctuation torque, and there is also a case where the opening and closing timing of the valve is fixed to the most delay angle phase when starting the internal combustion engine.
In addition, in the valve opening and closing timing control mechanism provided with the lock mechanism which holds the opening and closing timing at the intermediate phase, for example, in a case where the locked state of the lock mechanism cannot be released due to a failure, there is also a case where the opening and closing timing is fixed to the intermediate phase.
Furthermore, although the insufficiency of the hydraulic pressure of the hydraulic oil has been described as a type of the failure in which the valve opening and closing timing control mechanism does not appropriately operate, a mechanical failure on the inside of the valve opening and closing timing control mechanism may be considered, and even in a case where the valve opening and closing timing control mechanism does not appropriately operate due to a mechanical malfunction, there is also a case where the opening and closing timing (valve timing) is fixed to the most delay angle phase or the intermediate phase.
The valve opening and closing timing control mechanism is provided to control the opening and closing timing of the intake valve in many cases, and in a case where the opening and closing timing falls into the situation of being fixed to the most delay angle phase due to a failure, an intake air amount decreases, and thus, a compression ratio decreases, and not only the startability of the internal combustion engine deteriorates but also the combustion after the starting is made unstable.
In addition, in a case where the opening and closing timing (valve timing) of the intake valve is fixed to the intermediate phase due to a failure, the intake air amount when starting the internal combustion engine is not insufficient, and thus, although a necessary compression ratio is ensured, an overlap state where the exhaust valve and the intake valve are open at the same time is fixed. In such a situation where the overlap state is fixed, the combustion after the start of the internal combustion engine becomes unstable.
In other words, in the overlap state, since the combustion is continued by supplying the fuel to the combustion chamber in a state where a part of the combustion gas remains in the combustion chamber (state of the internal EGR), the fresh air becomes insufficient and the combustion becomes unstable. In particular, in a case of starting the internal combustion engine in a situation where the temperature of the internal combustion engine is higher than a set value and the overlap state is fixed due to a failure, there is also a case where the abnormal combustion is caused and the starting is not appropriately performed.
Furthermore, there is also a case where the valve opening and closing timing control mechanism is provided to control the opening and closing timing (valve timing) of the exhaust valve. In a case where the opening and closing timing of the valve opening and closing timing control mechanism provided in this manner is fixed to the most delay angle phase due to a failure, the overlap state where the exhaust valve and the intake valve are open at the same time is created, and thus, there is a case where the combustion after the starting becomes unstable due to the above-described reason.
Thus, a need exists for a controller for an internal combustion engine which is not susceptible to the drawback mentioned above.